Study has been forwarded in recent years concerning a TLC/SIMS method to analyze sample components held by a TLC plate relying upon a secondary ion mass spectroscopy (SIMS). This method can easily analyze a sparringly volatile mixture without using liquid chromatography, and hence is expected to come into general use in the future.
According to the thin layer chromatography, the plate is made up of a substrate such as of aluminum and an adsorption layer such as of silica gel formed on the surface of the substrate. A mixture sample is added to an end of the plate, and the end is dipped in a developing solvent, whereby the mixture is developed with the developing solvent and is separated into individual components.
The plate which carries the thus separated sample components is set to a predetermined position in the mass spectrometer, and is so moved that the sample components carried on the surface thereof successively pass through a position where they are bombarded with a primary beam.
Upon bombardment with the primary beam such as ion beam, the sample components are sputtered, and ions formed by the sputtering are subjected to mass dispersion due to the magnetic field. Among the ions, only those ions having a particular mass number are detected by a detector. Further, the intensity of the magnetic field or the ion acceleration voltage is swept, to successively detect ions having various mass numbers.
As the sample components are sputtered by the primary beam, generation of ions therefrom decreases gradually. In order to prevent this phenomenon, a matrix such as glycerol is applied onto the surface of the plate prior to setting the plate to a predetermined position in the mass spectrometer. The sample components are partly made lower as they are sputtered by the primary beam. Here, the matrix promotes the migration of the surrounding sample components into the reduced portion, so that generation of ions is prevented from decreasing.
According to the above-mentioned method, the TLC plate is continuously moved, and the primary beam keeps falling on the target at all times. Therefore, the primary beam falls even on those portions other than the sample components on the target, whereby undesired neutrons and ions are produced by the matrix on the portions other than the sample components. These particles contaminate the parts such as slits to deteriorate the performance of mass spectrometry.